| dc.description.abstract | About 70-80% of the world population relies on herbal products, especially in the developing
countries. Herbal products are available in various dosage forms for different types of ailment.
The genus Tephrosia is highly used worldwide as a remedy for numerous ailments, including
malaria, cancer, healing bleeding piles and wounds.
Contamination of herbal medicines by heavy metal is of great concern worldwide. Heavy metals
are known to affect the normal physiological function of plants or animals at elevated
concentrations.
In this study, the level of six heavy metals (Cd, Cr, Cu, Fe, Pb, Zn) were determined in soils and
plant parts (i.e. aerial part and root) of nine selected species of the genus Tephrosia: namely T.
purpurea, T. villosa, T. hildebrandtii, T. holstii, T. polyphylla, T. pumila, T. subtriflora, T. elata,
T. aequilata growing in South Eastern (Kilungu and Emali) and Coastal regions (Manyani, Kilifi
and Ukunda) of Kenya. Soil properties such as pH, organic matter and soil texture were also
determined for soils from the study sites.
The accumulation of the metals from soil to plants was also calculated in terms of Enrichment
Factor (EF), Translocation Factor (TF) and Bioaccumulation Factor (BF). Plant samples were
collected from the selected sites, washed, air- dried and milled. The samples were then digested
by wet digestion method and analyzed by Atomic Absorption Spectrophotometric technique
using Spectra AA-10.
Results showed that the medicinal herbs contained heavy metals namely: iron, chromium,
copper, zinc and lead. The concentration (mg/kg) ranges of heavy metals in the aerial part were
found to be as follows: chromium (0.06 to 1.49), iron (308.03 to 2077.57), copper (5.06 to 9.11),
zinc (7.58 to 20.77), cadmium (≤ 0.006), and lead (0.21 to 7.18). The concentration (mg/kg)
ranges of heavy metals in the roots were found to be as follows: chromium (<0.01 to 1.56), iron
(83.23 to 2104.9), copper (3.32 to 14.07), zinc (3.1 to 29.22), cadmium (≤ 0.006), and lead (≤
0.02 to 10.85). The concentration (mg/kg) of heavy metals in the soil sample was found to be as
follows: chromium (0.07 to 119.14), iron (2438.9 to 12, 485. 57), copper (1.33 to 23.71), zinc
(2.28 to 28.40), cadmium (≤ 0.006), and lead (0.33 to 4.53). The bioaccumulation factor ranged
from 0.00 to 7.42 with chromium recording the lowest BF and lead recording the highest BF at
Manyani in T. pumila. Enrichment factor ranged from 0.00 to 5.33 with chromium recording the lowest EF and zinc recording the highest EF at Kilifi in T. purpurea. Translocation factor ranged
from 0.00 to 16.67. BF, TF, and EF ranged from metal to metal.
Among the soil properties, pH ranged from 4.70 to 7.71, whereas the percentage Total Organic
Carbon ranged from 0.68 to 1.49. There was a negative correlation between soil pH and the
mean heavy metal concentrations; a positive correlation between the TOC and the mean heavy
metal concentrations. From the comparison of the results with the defined permissible limits, it
was concluded that the levels of heavy metals in the herbal plants were within the permissible
range for consumed medicinal herbs as defined internationally by the three different agencies
namely the USEPA, Codex Alimentarius Commission and WHO/FAO. Further studies could be
conducted to determine the metal speciation in the plant preparations since toxicity of metals
varies with oxidation states. To reduce bioaccumulation of heavy metals in human, a regular
monitoring programme is recommended to assess heavy metals in herbal medicines. Areas with
high levels of heavy metals such as Emali should not be used as sources for herbal medicine.
These data are of immediate interest to herbalists and medicinal practitioners in Kenya. Further,
awareness creation activities should be promoted to sensitize the physicians, and the general
public about the risk associated with consumption of herbal drugs contaminated with heavy
metals. | en_US |
